US Vice President Joe Biden (l.) and Japan's Prime Minister Shinzo Abe (r.) arrive at a joint news conference following their meeting at the prime minister's official residence in Tokyo December 3, 2013.

Toru Hanai/REUTERS

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Tokyo — US Vice President Joe Biden has voiced “deep concern” over China’s recent declaration of an air-defense identification zone (ADIZ) in the East China Sea, saying the move had raised regional tensions and the risk of accidents and miscalculations.

Mr. Biden, who is in Tokyo at the start of a week-long regional visit that will include China and South Korea, joined Japan’s prime minister, Shinzo Abe, in criticizing the zone, which includes the Senkaku Island chain – known as the Diaoyu in China – which are claimed by both Japan and China.

Aircraft operating inside the zone must first notify Chinese authorities of their flight plan, or face “defensive emergency measures.” China’s move has prompted fears that an accident involving Chinese and Japanese aircraft in the area could quickly escalate into an armed conflict.

On Tuesday, Biden told a joint news conference with Mr. Abe that the US was “deeply concerned by the attempt to unilaterally change the status quo in the East China Sea.

“This action has raised tensions and increased the risk of accidents and miscalculation. We are closely consulting with our allies here in Japan and in Korea.”

Abe said Japan and the US would coordinate their response. “We should not tolerate the attempt by China to change the status quo unilaterally by force,” he said. “We will continue to work closely in dealing with the situation based on a strong US-Japan alliance.”

Despite their show of unity, Tokyo and Washington have adopted slightly different responses to China’s demands. Hackles were raised in Japan after it emerged that three US commercial airlines, acting on government advice, were complying with Chinese requests for flight-path information.

Japan’s government, by contrast, has urged its civilian airlines to defy the regulations.

The US State Department insisted, however, that its advice to airliners did “not indicate US government acceptance of China’s requirements.” To demonstrate its opposition, the US last week flew two B-52 bombers into the area without notifying Chinese authorities.

"Our general position as a US government is that we don't accept China's requirements," US state department spokeswoman Jen Psaki said on Monday.

Chinese officials were quick to exploit the minor rift. Hong Lei, a foreign ministry spokesman, told reporters in Beijing that the US had showed a “constructive attitude,” but dismissed Japan’s “erroneous actions.”

Speaking to reporters after their press conference, Biden and Abe attempted to play down any dispute over actions by their countries’ airlines. “We further agreed we will not condone any actions that could threaten safety of civilian aircraft," Abe said.

Diplomatic balancing act

Since arriving in Japan on Monday, Biden has been performing a delicate diplomatic balancing act. He does not want to alienate China, whose leader, Xi Jinping, he is expected to meet later this week, but at the same time he has toreassure Japan that it has the US’s unequivocal support in the zone row.

In an editorial, China's official Global Times newspaper warned Biden against offering unrestrained support for Japan’s position on the air defense zone.

"The only choice he has if he wants a successful trip [to China] is not to go too far in his words over there," it said. "If he openly supports Tokyo and wants to 'send an expedition to punish' Beijing, the Chinese people won't accept it."

Biden stopped short of calling on Beijing to scrap the zone altogether and called for better crisis management mechanisms between Japan and China, whose leaders have not held official talks since taking office.

Washington has refused to take sides in the dispute over the Senkaku Islands, a strategically important archipelago surrounded by rich fishing grounds and potentially large gas and mineral deposits.

But its security treaty obligations requires the US to come to Japan’s defense should the diplomatic spat turn into a military conflict.

While that seems unlikely, Tobias Harris, a Washington-based Japan specialist at Teneo, an independent advisory firm, said much would depend on how China reacts to unidentified aircraft flying inside the zone.

“With China doing the same, the probability of a lethal confrontation between the two air forces, while still low, has increased. The danger of the Chinese ADIZ will depend in part on how aggressively China responds to unidentified aircraft.”

The rift between northeast Asia’s two biggest economies is an unwelcome distraction for the US as the Obama administration attempts to shift its foreign policy focus to the Asia-Pacific.

"Yes, some question our staying power," Biden said in an interview with Japan's Asahi Shimbun newspaper. "But Japan knows that we have stayed for more than 60 years, providing the security that made possible the region's economic miracle. Economically, diplomatically, militarily, we have been, we are, and we will remain a resident Pacific power."